Measuring Eathquakes (back to homepage) Vocabulary focus- the point beneath Earth's surface, where rock that is under stress breaks, triggering an earthquake epicenter- the point on the surface directly above the focus seismic wave-a vibration that travels through Earth carrying the energy released during an earthquake Primary Wave- an earthquake squeezes and st5retches the ground like an accordian
(P Wave) Secondary Wave- a kind of wave that vibrates side to side, and up and down
(S Wave) surface wave-a kind of seismic wave that is produced when S and P waves arrive at the center of the Earth magnitude- the measurement of the strength of and earthquake based on seismic waves and the movements along the faults Mercalli Scale- a scale that grades an earthquake by the amount of damage they cause Ritcher Scale- a scale that evaluates seismic waves as measured by a certain sort of mechanical seismograph moment magnitude scale-a scale that rates earth quakes by estimating the total energy released by a earthquake Outline
*Seismic Waves*
during an earthquake, seismic waves dash out of the focus
they carry the energy of an earthquake through the interior, and onto the surface
three types:P wave, S wave, and surface wave
when these waves touch the Earth's surface at the epicenter, surface waves are produced
Primary Waves
moves straight forward
causes buildings to contract and expand
they come first
can move through solid and liquid
Secondary Waves
they come second
move side to side and up and down
shakes violently
can only move through solids
Surface Waves
when S and P waves come to surface, some become surface wave
make most severe ground movement
some make the ground move like rolling waves
Some make buildings shake side to side
Detecting Seismic Waves
use seismograph to record and measure the vibration and shaking of seismic wave
a seismograph needs a pen, a rotating drum, support,and weight
during an earthquake, the drum is shaken by seismic waves; the pen stays steady while the drum moves, ao that the pen draws the vibrations
now, scientists use electric seismographs
Measuring Earthquakes
at least 20 different measures for rating earthquakes
The Mercalli Scale
in 20 century it was invented to rate earthquakes according to their intensity
not precise
all 12 steps show how earthquakes affect people, buildings, and land surface
the same quake can have different Mercalli rating, because it causes different amounts of damage in different spots----
The Mercalli Scale
|| 1~2 || Almost unnoticeable ||
|| 3~4 || Unstable objects disturbed (people notice vibrations like those passing from a truck ||
|| 5~6 || Slight damage (dishes and windows rattle, books are being knocked off shelves) ||
|| 7~8 || Moderate heavy damage (people run outdoors) ||
|| 9~10 || Cracks and landslides appear in the ground (buildings that fall off foundations are destroyed ||
|| 11~12 || Severe Damage (wide cracks appear in ground,waves visible on surface)
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*The Ritcher Scale*
measures waves by a certain kind of mechanical seismograph
meaures the size of the seismic waves
*Moment Magnitude Scale*
meaures earthquakes by measuring the total energy released
Measuring Eathquakes (back to homepage)
Vocabulary
focus- the point beneath Earth's surface, where rock that is under stress breaks, triggering an earthquake
epicenter- the point on the surface directly above the focus
seismic wave-a vibration that travels through Earth carrying the energy released during an earthquake
Primary Wave- an earthquake squeezes and st5retches the ground like an accordian
(P Wave)
Secondary Wave- a kind of wave that vibrates side to side, and up and down
(S Wave)
surface wave-a kind of seismic wave that is produced when S and P waves arrive at the center of the Earth
magnitude- the measurement of the strength of and earthquake based on seismic waves and the movements along the faults
Mercalli Scale- a scale that grades an earthquake by the amount of damage they cause
Ritcher Scale- a scale that evaluates seismic waves as measured by a certain sort of mechanical seismograph
moment magnitude scale-a scale that rates earth quakes by estimating the total energy released by a earthquake
Outline
The Mercalli Scale
|| 3~4 || Unstable objects disturbed (people notice vibrations like those passing from a truck ||
|| 5~6 || Slight damage (dishes and windows rattle, books are being knocked off shelves) ||
|| 7~8 || Moderate heavy damage (people run outdoors) ||
|| 9~10 || Cracks and landslides appear in the ground (buildings that fall off foundations are destroyed ||
|| 11~12 || Severe Damage (wide cracks appear in ground,waves visible on surface)
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Diagrams
WD = Wave Direction